Gradient coil assembly for a magnetic resonance imaging device and magnetic resonance imaging device

ABSTRACT

A gradient coil assembly for a magnetic resonance imaging device is disclosed. The gradient coil assembly comprises a cylindrical carrier with conductors forming three gradient coils associated with three orthogonal physical gradient axes. The cylindrical carrier comprises at least two radial through openings at different angular positions. At least one of the conductors runs through at least one area of the carrier located circumferentially between the through openings.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of Europepatent application no. EP21197316, filed on Sep. 17, 2021, the contentsof which are incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure concerns a gradient coil assembly for a magneticresonance imaging device, comprising a cylindrical carrier withconductors forming three gradient coils associated with three orthogonalphysical gradient axes. The disclosure further concerns a magneticresonance imaging device having such a gradient coil assembly.

BACKGROUND

Magnetic resonance imaging (MRI) has become an often-used imagingmodality, in particular in medicine. MRI requires a main magnetic fieldof high field strength and high homogeneity. With respect to magneticfield quality, cylindrical magnetic resonance imaging devices are mostlypreferred. Such magnetic resonance imaging devices usually comprise anat least essentially cylindrical main magnet assembly, wheresuperconducting main field coils are provided in a vacuum chamber, inparticular cooled by helium. The main magnet assembly defines acylindrical central opening, in which a gradient coil assembly forproviding gradient fields, in particular for spatial encoding and,often, a radio frequency coil assembly, for example comprising a bodycoil, are received. This arrangement may then be covered by coverelements, such that the patient bore remains open for receiving apatient to be imaged. That is, radially outwards from the patient, aradio frequency (RF) coil assembly, a gradient coil assembly, and themain magnet assembly follow each other.

In most known magnetic resonance imaging devices, the patient in thebore is only accessible through the axial openings of the bore. However,for many medical applications, better access to the patient is desired.For example, access to an imaging volume in the patient may be expedientfor other imaging modalities, for example x-ray imaging or PET imaging,and/or for therapy, for example radiation therapy.

To provide such access for medical applications to be combined withmagnetic resonance imaging, it has been proposed to split at least thegradient coil assembly into two halves, such that, in the area of thefield of view of the magnetic resonance imaging device, a free space,which could be used for placement of medical imaging or therapy devicesor to allow such devices to access the field of view in the patient, isprovided.

In an article by R. Fahrig et al., “A truly hybrid interventionalMR/X-ray system: Feasibility demonstration”, J Magn Reson Imaging 13(2001), pages 294-300, the technical issues related to acquisition ofx-ray images inside an open MRI system were studied. A flat-panel x-raydetector was placed under the patient bed, a fixed anode x-ray tubeoverhead with the anode-cathode axis aligned with the main magneticfield and a high frequency x-ray generator. High-quality x-ray and MRimages have been acquired without repositioning the object using thehybrid system.

In an article by Poole et al., “Split gradient coils for simultaneousPET-MRI”, Magn Reson Med. 62 (2009), pages 1106-11, it was proposed toplace the positron emission tomography detection scintillating crystalsin an 80 mm gap between two halves of a 1 T split-magnet cryostat. Anovel set of gradient and shim coils has been specially designed for thesplit MRI scanner to include an 110 mm gap from which wires are excludedso as not to interfere with positron detection.

However, split gradient coils result in a number of disadvantages. Theseinclude, for example, lower sensitivity and the requirement of torquecompensation for the halves, leading to a further reduction insensitivity and complicating the shielding of the stray field withregard to the main magnet.

SUMMARY

It is an object of the current disclosure to provide an improved designfor gradient coil assemblies for magnetic resonance imaging devices,which, on the one hand, provides access for other diagnostic and/ortherapeutic modalities and, on the other hand, provides high sensitivityand good shielding.

In a gradient coil assembly as initially described, this object isachieved by the carrier comprising at least two radial through openingsat different angular positions, wherein at least one of the conductorsruns through at least one area of the carrier located circumferentiallybetween the through openings.

It is an insight of the current disclosure that for many medicalapplications, e.g. imaging and/or therapeutic modalities, to be combinedwith magnetic resonance imaging, access over the full 360 degreesazimuthal angle is not required. Instead, access at a finite number ofpositions, for example two or four orthogonal positions, is sufficientfor many medical applications. Hence, a gradient coil assembly isproposed, which provides access to the field of view of the magneticresonance device at at least two angular positions. The area betweenthese access points, that is, the through openings, still leaves enoughroom for the usual carrier structure, e.g. the placement of conductors,strongly reducing the effect of the through openings compared with acompletely split gradient coil assembly.

In other words, the access for other diagnostic and/or therapeuticmodalities, such as for example, x-ray, PET, radiation therapy (LINAC)and the like, is provided by spatially limited through openings, thatis, apertures, which act as passages for radiation and/or particlesand/or instruments and/or installation location for medical imagingand/or therapy devices. This replaces a circumferential gap between twohalves. The areas circumferentially located between thespatially-limited through openings can be used for conductors of thegradient coils to provide a higher sensitivity (mT/m/A) for the gradientcoils. Hence, a reduction of gradient coil efficiency and gradient fieldquality can be reduced to a required minimum. Furthermore, themechanical stability is improved, since it is no longer necessary toprevent twisting of the halves against each other.

The through openings (apertures) are (e.g. all) located in the sameaxial plane of the carrier and/or at an axial center of the carrier,e.g. in a central axial plane, where, usually, the field of view(homogeneity volume) of the magnetic resonance device is located. Hence,the through openings provide access to the field of view of the magneticresonance imaging device.

The carrier can be constructed using known implementations. Forinstance, conductors (and optionally other layers) may be placed onplates, from which the carrier is then formed by casting a carriermaterial, e.g. a resin, around this arrangement. Such methods are, inprinciple, known in the art and do not have to be discussed in detailhere.

In embodiments, at least one, e.g. all, of the through openings arelocated at an angular position of minimal electric current density. Thatis, the through openings may be positioned in areas where, by design,the number of conductors of the gradient coil would be very low.However, usually if the physical gradient axes are chosen as the axialdirection (e.g. the z direction), the vertical direction (e.g. the ydirection) and the horizontal direction (e.g. the x-direction), theangular positions of highest conductor density, and thus highest currentdensity, would be at 0 degrees (uppermost vertical position), 90degrees, 180 degrees, and 270 degrees. On the other hand, these arepreferred positions for access of other medical imaging and/or therapymodalities. For example, medical professionals using a bi-plane x-raysystem often use x-ray imaging arrangements oriented along the verticalaxis (0 degrees) and along the horizontal axis (90 degrees). In thismanner, images acquired by a medical imaging device and/or therapymeasures provided by a medical therapy device can be easier understoodand interpreted by the medical staff. For instance, placement at 0degrees (vertical direction) and 90 degrees (horizontal direction) areknown to the user and are intuitive.

It is noted at this point that also generally at least one pair ofthrough openings, e.g. all adjacent through openings, are provided at anangular distance of 90 degrees. For example, regarding x-rayapplications, in this manner two orthogonal x-ray projection images maybe acquired.

To place the through openings in an angular section where only fewconductors of the gradient coils would be required for a suitabledesign, as explained above, in embodiments of the disclosure the angularpositions of the through openings are located centrally between twophysical gradient axes in the axial plane of the through openings. Thatis, the through openings have centers at 45 degrees to each of the axes,such that, also in this case, adjacent through openings are angularlydisplaced by 90 degrees. In an embodiment, four through openings may beprovided, one in each quadrant formed by the two physical gradient axesin the axial plane of the through openings. This provides a highsymmetry advantageous in coil design and may, for example in an x-rayapplication, be used to place a transmitter and a receiver opposingly.

As already noted, e.g. at least one through opening provides verticalaccess (e.g. 0 degrees) and at least one through opening provideshorizontal access (e.g. 90 degrees). These angular positions match thelocations where the transverse physical gradient axes, if chosen ashorizontally (e.g. the x direction) and vertically (e.g. the ydirection) as usual, comprise the maximal current density such that adisruption at these angular positions would be nearly as disadvantageousas a complete split. To solve this problem, as will be further discussedwith regard the magnetic resonance imaging device according to thedisclosure, it is proposed to rotate the transverse gradient axes by 45degrees in the axial planes, such that the through openings are not inan area with maximum current density, but with minimum current density.Together with the third physical gradient axes in the axial direction,such a set of physical gradient axes still forms an orthogonal set ofgradients. For magnetic resonance imaging, these physical gradient axes,which run diagonally, can be easily combined to logical gradient axes,which, as usual, run in the horizontal direction (e.g. the x direction)and in the vertical direction (e.g. the y direction). Such reprocessingto logical gradient axes is, for example, known from methods foracquisition of tilted slices.

In embodiments, the gradient coil assembly may further comprise at leastone electrical shield, which is usually positioned radially outward fromthe conductors forming the gradient coils, i.e. towards the main magnetassembly in the magnetic resonance imaging device. In an embodiment, theshield may also extend at least partially (e.g. completely), through atleast one of the areas of the carrier located circumferentially betweenthe through openings.

In embodiments, the shield may comprise an active shielding coilarrangement electrically connected to the gradient coils, wherein atleast one electrical connection between the shield and the gradientcoils runs through at least one of the through openings. That is, thegradient coil assembly comprises two layers of coils: an inner layerproviding the gradient coils and an outer layer providing the activeshielding coils. The active shielding coils actively counteract thefield generation of the gradient coils to the radially outer side, as isgenerally known. The presence of the through openings can now be used tofurther increase the efficiency of the gradient coil assembly. In thisembodiment, the through openings are additionally used to directlycontact the primary layer (gradient coils) to the secondary (shielding)layer (active shielding coils). In this manner, the inductance of thegradient coil is advantageously reduced such that the efficiency of agradient coil assembly with through openings is only slightly less thanthe efficiency of a conventional gradient coil assembly having nothrough opening.

As one example, as is generally known, the course of the conductors(e.g. also for the electrical shield) may be determined computationallyby an optimization algorithm running on at least one processor. Hence,the conductors may be arranged on the carrier according to a patterngenerated using the presence of the through openings as a boundarycondition, e.g. also providing an interlayer connection surface. Thatis, the surfaces of the walls emitting the through openings may beincluded as an interlayer connection surface where conductors connectingthe gradient coils and the active shielding coils run. In this manner,the presence of the through openings can optimally be exploited by wayof design, providing a highly efficient, low inductance gradient coilassembly comparable in performance to a gradient coil assembly having noaccess options for further medical applications.

Regarding the dimensions of the through openings, these may be selectedcorresponding to a field of view of a medical imaging device using thethrough openings, for example an x-ray imaging device. For example, if acone-beam geometry is used for x-ray imaging, the dimensions of thethrough openings may be selected to accommodate the cone-beam emittedfrom an x-ray source emitting its x-rays through at least one of thethrough openings. The through opening provides enough space toaccommodate the x-ray radiation field. In the example of a radiationtherapy device, for example, a particle or photon beam-sized throughopening may be provided.

Generally speaking, the through openings may, for example, extend overany suitable angular interval (e.g. of 5 to 15 degrees) in thecircumferential direction, such that only a minor part of the fullangular interval is used for these apertures.

The disclosure further concerns a magnetic resonance imaging device,comprising a gradient coil assembly according to the disclosure and amain magnet assembly having openings aligned with the through openingsof the carrier, wherein at least one medical imaging and/or therapydevice is at the last partly received in at least one set of alignedopenings. All features and remarks regarding the gradient coil assemblyanalogously apply to the magnetic resonance imaging device, such thatthe same advantages can be achieved.

In most cases, the through openings are used for providing access to thefield of view of the magnetic resonance imaging device, that is, thehomogeneity volume, for example for radiation, particles, and/orinstruments. The corresponding medical imaging and/or therapy devices,in most cases, may be placed radially outside the gradient coilassemblies, for example in corresponding openings in the main magnetassembly. However, in some cases, these may also be at least partlyplaced in the through openings. Generally speaking, the openings in themain magnet assembly do not have to be complete through openings and/ormay have different dimensions from the through holes, for example belarger depending on the additional medical application to beimplemented.

In embodiments, the magnetic resonance imaging device may furthercomprise a cylindrical radio frequency coil assembly inside the carrier,which also has through openings aligned with the through openings of thecarrier. As already explained, such a radio frequency coil assembly may,for example, comprise a body coil for sending radio frequency pulsesand/or receiving magnetic resonance signals. If the medical imagingand/or therapy device uses radiation and/or particles able to passthrough the materials of such a radio frequency coil assembly, throughopenings may, in other embodiments, also not be necessary.

In embodiments, the magnetic resonance imaging device may furthercomprise a patient table, wherein at least the gradient coil assembly isrotatable around the patient table. Preferably, the main magnet assemblyand the gradient coil assembly, e.g. also the radio frequency coilassembly, may be rotatable together around the patient table. If atleast the gradient coil assembly is rotatable around the axialdirection, a more flexible geometry may be realized. For example, ifmagnetic resonance imaging and the additional modality provided by theat least one medical imaging and/or therapy device are to be appliedsuccessively in time, the gradient coil assembly may be used in a basicposition for the additional modality, and in a position rotated 45degrees for magnetic resonance imaging, such that the physical gradientaxes comprise a vertical and a horizontal axis.

As already discussed regarding the gradient coil assembly, the throughopenings of the gradient coil assembly may e.g. be positioned at arelative angular position of 45 degrees to the respective physicalgradient axes. Here, the influence on the efficiency of the gradientcoils is reduced. Since, however, the most intuitive positioning forthrough openings and thus the additional imaging and/or therapy modalityto be combined with magnetic resonance imaging are the horizontal andvertical directions (90 degrees and 0 degrees), the physical gradientaxes may advantageously run diagonally.

In such a configuration, in an embodiment, the magnetic resonanceimaging device may further comprise a control device, wherein the twophysical gradient axes perpendicular to the longitudinal axis (e.g. theaxial or z direction) are at angles of 45 degrees each to the horizontaland the vertical direction (e.g. the x and y direction), where theopenings align, and the control device is configured to process acquiredmagnetic resonance data to a logical vertical and a logical horizontalgradient axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present disclosure will becomeapparent from the following detailed description considered inconjunction with the accompanying drawings. The drawings, however, areonly principle sketches designed solely for the purpose of illustrationand do not limit the disclosure. The drawings show:

FIG. 1 illustrates an exemplary perspective view of a gradient coilassembly according to one or more embodiments of the disclosure;

FIG. 2 illustrates an exemplary side view of the gradient coil assemblyof FIG. 1 , according to one or more embodiments of the disclosure;

FIG. 3 illustrates an exemplary schematic section view along the lineIII-III in FIG. 2 , according to one or more embodiments of thedisclosure;

FIG. 4 illustrates an exemplary conductor pattern of the gradient coilassembly of FIG. 1 , according to one or more embodiments of thedisclosure;

FIG. 5 illustrates a conventional first rolled out depiction of anoctant of a transverse gradient layer;

FIG. 6 illustrates an exemplary conductor pattern modified from thatshown in FIG. 5 , with rotated physical gradient axes, according to oneor more embodiments of the disclosure; and

FIG. 7 illustrates an exemplary principle view of a magnetic resonanceimaging device, according to one or more embodiments of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 illustrates an exemplary perspective view of a gradient coilassembly according to one or more embodiments of the disclosure. FIG. 1shows a perspective view of a gradient coil assembly 1 according to thedisclosure. As can be seen, the gradient coil assembly 1 comprises acylindrical carrier 2 extending in an axial direction 3 along arespective longitudinal axis. Additionally, a horizontal direction 4 anda vertical direction 5 are shown. In magnetic resonance imaging devices,the longitudinal axis 3 usually is a z direction, i.e. the horizontaldirection 4 is the x direction, and the vertical direction 5 is the ydirection. In FIG. 1 and the following Figures, the gradient coilassembly 1 is shown in an orientation in which it is inserted into anaperture of a main magnet assembly of a magnetic resonance imagingdevice. Here, the vertical upwards direction corresponds to 0 degrees,and a horizontal sidewards direction to 90 degrees. In a central axialplane comprising the homogeneity volume, and thus the field of view ofthe magnetic resonance imaging device, through openings 6 are providedat 0 degrees, 90 degrees, 180 degrees, and 270 degrees, which are thusangularly spaced apart by 90 degrees each. These through openings 6(apertures) are provided as access points for an additional diagnosticor therapeutic modality, that is, an additional medical application, forexample x-ray imaging, radiation therapy or PET imaging.

Their dimensions are chosen sufficiently for the respective additionalmodality to be combined with magnetic resonance imaging, e.g. forsimultaneous use. For example, if x-ray imaging is used, where, forexample, an x-ray source may be placed in a correspondingly alignedopening of the main magnet assembly, the x-ray radiation fielddimensions, for example a cone-beam, may define the dimensions of thethrough openings 6. While, in this example, the x-ray detector may beplaced in or behind the opposing through openings 6, the x-ray detectormay also be placed inside the bore of the magnetic resonance imagingdevice, adjacent to the patient, while the opposing through openings 6serve to provide symmetry advantageous for the design and efficiency ofthe gradient coil assembly 1, as further discussed below. Generally,however, choosing the horizontal direction 4 and the vertical direction5 for the additional diagnostic and/or therapeutic modality provides forintuitive use by medical staff.

As can be seen in the cross-sectional view through the central axialplane 7 indicated in FIG. 2 , the carrier 2 comprises at least onecarrier material 8, and conductors 9 are coarsely indicated in FIG. 3for ease of explanation.

An exemplary conductor configuration and pattern is shown in FIG. 4 ,where it can be seen that the conductors 9 are arranged in two layers,namely an inner layer 10 and an outer layer 11. Conductors of the innerlayer 10 form the gradient coils for three physical gradient axesprovided by the gradient coil assembly 1. In this embodiment, thephysical gradient axes 12 perpendicular to the longitudinal direction 3have been rotated from their usual orientation along the horizontaldirection 4 and the vertical direction 5 by 45 degrees, and hence rundiagonally. This is due to the positioning of the through openings 6, asexplained with respect to FIGS. 5 and 6 .

FIG. 5 shows a conventional conductor pattern of a transverse gradientcoil in one octant rolled out on the plane spanned by the longitudinaldirection 3 and the circumferential direction. If, a through opening, asindicated by box 13, is positioned to provide access in a vertical orhorizontal direction, the through opening would thus be positioned in anarea of very high conductor density and thus current density, inparticular maximum current density, such that the efficiency of thegradient coil would be strongly reduced by placing a through opening 6here.

However, if the angular positions of the through openings 6 are rotated45 degrees against the physical gradient axis 12, a position of lowcurrent density, in particular minimum current density, is reached, andthe conductor pattern can, as shown in FIG. 6 , be designed to maintaina high efficiency of the gradient coils and hence the complete gradientcoil assembly 1. It is noted that the conductor patterns of FIG. 5 andFIG. 6 only show one gradient coil, while the transverse gradient coilfor the perpendicular transverse gradient axis 12 would have its currentdensity maximum at an angular distance of 90 degrees, that is, the rightedge of the octant shown in FIGS. 5 and 6 , such that the angularposition of 45 degrees is the one with minimum current density if allgradient coils are taken into account.

In the magnetic resonance imaging device, a control device may beconfigured to process acquired magnetic resonance data to use logicalgradient axes in the horizontal and vertical directions 4, 5 instead ofthe tilted physical gradient axes 12.

The conductors of the outer layer 11 form active shielding coils, thatis, the outer layer 11 represents an electrical shield of the gradientcoil assembly 1. These active shielding coils actively counteract theelectromagnetic fields of the gradient coils in the inner layer 10 inthe radially outward direction, that is, to the main magnet unit, inaccordance with known principles.

The active shielding coils and the gradient coils may be electricallyconnected, e.g. to reduce the inductance of the gradient coil assembly.In this embodiment, the presence of the through openings 6 is used toprovide additional electrical contacting options, e.g. an additionalsurface for conductors 9 electrically connecting the layers 10, 11, ascan be seen in FIG. 4 for the leftmost through opening 6. In otherwords, the primary layer 10 and the secondary (shielding) layer 11, e.g.gradient coils and active shielding coils associated with respectivephysical gradient axes 12 are directly electrically connected via thethrough openings 6, e.g. their wall surfaces as interlayer connectionsurfaces. In this manner, the inductance of the gradient coils isreduced, increasing the efficiency of the gradient coil assembly 1.

It is noted that the presence of the through openings 6, and hence theinterlayer connection surfaces, may also be taken into account whendesigning the conductor pattern for the gradient coil assembly 1.

FIG. 7 shows an exemplary schematic cross-sectional view of a magneticresonance imaging device 14 according the disclosure. The magneticresonance imaging device 14 comprises a radially outer, at leastpredominantly cylindrical main magnet assembly 15, in which a gradientcoil assembly 1 according to the disclosure and an optional radiofrequency (RF) coil assembly 16 are received, leaving an open areaforming the patient bore 17. Using a patient table 18, an imaging regionof the patient can be positioned in the schematically indicatedhomogeneity volume 19, that is, the field of view of the magneticresonance imaging device 14.

The RF coil assembly 16 comprises through openings 20 aligned with thethrough openings 6 of the gradient coil assembly 1. Furthermore, themain magnet assembly 15 comprises openings 21, which do not have to bethrough openings, aligned with through openings 6 and 20. In theembodiment shown here, medical imaging and/or therapy devices 22 for theadditional diagnostic and/or therapeutic modality to be combined withmagnetic resonance imaging, for example x-ray imaging components like anx-ray source, are mounted in at least two of the openings 21, allowingaccess to the homogeneity volume 19 from vertical direction 5 and fromhorizontal direction 4. In other embodiments, medical imaging and/ortherapy devices 22 may also be at least partly received in throughopenings 6 and/or 20. In the embodiment shown in FIG. 7 , radiationand/or particles and/or instruments by the medical imaging and/ortherapy devices 22 may pass through the through openings 6 and 20towards or from the homogeneity volume 19.

Since, as explained with respect to FIG. 4 , the physical gradient axes12 run diagonally, that is at 45 degrees to the vertical direction 5 andthe horizontal direction 4, a control device 23 of the magneticresonance imaging device 14 is configured to process magnetic resonancedata from these physical gradient axis 12 to logical gradient axes inthe horizontal and vertical directions 4, 5.

Although the present disclosure has been described in detail withreference to the preferred embodiments, the present disclosure is notlimited by the disclosed examples from which the skilled person is ableto derive other variations without departing from the scope of thedisclosure.

The various components described herein may be referred to as “devices”or “units.” Such components may be implemented via any suitablecombination of hardware and/or software components as applicable and/orknown to achieve the intended respective functionality. This may includemechanical and/or electrical components, processors, processingcircuitry, or other suitable hardware components configured to executeinstructions or computer programs that are stored on a suitable computerreadable medium. Regardless of the particular implementation, suchdevices and units, as applicable and relevant, may alternatively bereferred to herein as “circuitry,” “processors,” or “processingcircuitry.”

What is claimed is:
 1. A gradient coil assembly for a magnetic resonanceimaging device, comprising: a cylindrical carrier; and a set ofconductors forming three gradient coils, the set of conductors beingincluded in the cylindrical carrier, and each one of the three gradientcoils being associated with a respective one of three orthogonalphysical gradient axes, wherein the cylindrical carrier comprises tworadial through openings disposed at different angular positions withrespect to one another, and wherein a conductor from among the set ofconductors passes through an area of the cylindrical carrier that islocated circumferentially between the two radial through openings. 2.The gradient coil assembly according to claim 1, wherein one of the tworadial through openings is located at an angular position of minimalelectric current density.
 3. The gradient coil assembly according toclaim 2, wherein each one of the two radial through openings is locatedat an angular position of minimal electric current density.
 4. Thegradient coil assembly according to claim 1, wherein the two radialthrough openings are disposed at an angular position of 90 degrees withrespect to one another.
 5. The gradient coil assembly according to claim4, wherein the two radial through openings are from among a plurality ofradial through openings, and wherein each adjacent pair of radialthrough openings from among plurality of radial through openings aredisposed at an angular position of 90 degrees with respect to oneanother.
 6. The gradient coil assembly according to claim 1, wherein anangular position of each one of the two radial through openings iscentrally located between two physical gradient axes from among thethree orthogonal physical gradient axes in an axial plane containing thetwo radial through openings.
 7. The gradient coil assembly according toclaim 6, wherein the two radial through openings are from among fourradial through openings, and wherein each one of the four radial throughopenings is disposed in a respective quadrant formed by the two physicalgradient axes of the axial plane.
 8. The gradient coil assemblyaccording to claim 1, further comprising: an electrical shield.
 9. Thegradient coil assembly according to claim 8, wherein the electricalshield comprises an active shielding coil arrangement electricallyconnected to the three gradient coils, and wherein a connection betweenthe electrical shield and each one of the three gradient coils runsthrough one of the two radial through openings.
 10. The gradient coilassembly according to claim 1, wherein the set of conductors arearranged on the cylindrical carrier according to a pattern that isgenerated using a presence of the two radial through openings as aboundary condition.
 11. The gradient coil assembly according to claim10, wherein the set of conductors are arranged on the cylindricalcarrier according to the pattern that is generated by further definingsurfaces of walls associated with the two radial through openings as aninterlayer connection surface in which the set of conductors connectingeach one of the three gradient coils and the active shielding coils passthrough.
 12. The gradient coil assembly according to claim 1, whereinthe dimensions of the two radial through openings correspond to a fieldof view of a medical imaging device using the two radial throughopenings.
 13. The gradient coil assembly according to claim 1, whereinthe two radial through openings extend over an angular interval having arange between 5 to 15 degrees in a circumferential direction.
 14. Amagnetic resonance imaging device, comprising: a gradient coil assembly,comprising: a cylindrical carrier; and a set of conductors forming threegradient coils, the set of conductors being included in the cylindricalcarrier, and each one of the three gradient coils being associated witha respective one of three orthogonal physical gradient axes, wherein thecylindrical carrier comprises two radial through openings disposed atdifferent angular positions with respect to one another, and wherein aconductor from among the set of conductors passes through an area of thecylindrical carrier that is located circumferentially between the tworadial through openings; and a main magnet assembly having a set ofopenings, each opening from among the set of openings being aligned witha respective one of the two radial through openings of the cylindricalcarrier, and wherein a medical imaging device and/or therapy device isat least partly received in the set of openings.
 15. The magneticresonance imaging device according to claim 14, further comprising: acylindrical radio frequency (RF) coil assembly disposed inside thecylindrical carrier, wherein the cylindrical RF coil assembly has twothrough openings respectively aligned with the two radial throughopenings of the cylindrical carrier.
 16. The magnetic resonance imagingdevice according to claim 14, wherein the medical imaging devicecomprises an x-ray device for simultaneous acquisition of x-ray imagingdata and magnetic resonance imaging data.
 17. The magnetic resonanceimaging device according to claim 14, further comprising: a patienttable, wherein the gradient coil assembly is rotatable around thepatient table.
 18. The magnetic resonance imaging device according toclaim 17, wherein the main magnet assembly and the gradient coilassembly are rotatable together around the patient table.
 19. Themagnetic resonance imaging device according to claim 17, wherein themain magnet assembly, the gradient coil assembly, and the cylindrical RFcoil assembly are each rotatable around the patient table.
 20. Themagnetic resonance imaging device according to claim 14, furthercomprising: control circuitry, wherein two physical gradient axes fromamong the three orthogonal physical gradient axes are perpendicular to alongitudinal axis of the magnetic resonance imaging device and aredisposed at angles of 45 degrees relative to the horizontal and thevertical direction, respectively, where the two radial through openingsalign, and wherein the control circuitry is configured to processacquired magnetic resonance data to a logical vertical and a logicalhorizontal gradient axis.